1. Field of the Invention
The present invention relates to detergent compositions.
2. Description of the Prior Art
Recently, it has been recognized that phosphate surfactants, a kind of anionic surfactant, are very mild surfactants having a low stimulus to the skin. For this reason, they are employed as a component of detergent compositions.
However, such phosphate surfactants have several disadvantages such as deficiency of foaming ability, foaming power, and low-temperature stability, all of which are essential properties required for detergent compositions. Thus, they are not yet deemed satisfactory as surfactants for detergent compositions. Therefore, there has been a demand for improvements in the properties of detergent compositions containing phosphate surfactants while preserving the advantageous characteristics of phosphate.
Alkyl phosphate can generally be obtained as a mixture of monoalkyl phosphate and dialkyl phosphate; thus phosphate surfactants contain dialkyl phosphate having poor water solubility and poor foaming power. Accordingly, when these alkyl phosphates are used as a detergent base for shampoo or skin cleaner, it is necessary to use surfactants in which the monoester content is as much as possible or in which ethylene oxide is added to alkyl groups so as to increase water solubility.
In addition, since there are problems with respect to foaming power and low-temperature stability if such particular alkyl phosphates are singly used as the main components of the detergents, a method in which auxiliaries are further added to detergents has been proposed (Japanese Patent Publication No. 51991/1983, and Japanese Patent Application Laid-Open Nos. 49698/1982, 103598/1983, and 74196/1984).
However, although all of these methods may improve the properties compared with single use of an alkyl phosphate, there still remain problems in that foaming power and low-temperature stability are insufficient as compared with detergents containing other ordinary surfactants as a main agent, and in that the low irritation characteristic specific to alkyl phosphates is lost. Of these methods, a method in which sulfobetaine is used as an auxiliary (Japanese Patent Publication No. 51991/1983) is a relatively excellent method from the veiwpoint of the increase in foaming power and the improvement in low-temperature stability. However, according to this method, propanesultone, which involves some fear of carcinogenesis, must be used to produce the sulfobetaine, so that the method is quite disadvantageous to industrial production of the sulfobetaine.
Further, it should be noted that the phosphate surfactants are likely to give unfavorable feeling to touch to the hair because they produce a calcium salt as they contact with water when they are rinsed, and the salt is adhered to the hair to impair the smoothness of the hair. Thus, the phosphate surfactants are not necessarily satisfactory as surfactant usable for preparing detergent compositions including shampoo compositions.
In order to ameliorate these problems, a method in which a conditioning agent such as an oil is added to a shampoo base has been generally employed. However, this method involved problems in that the addition of the conditioning agent greatly decreases the foaming and cleaning power which are the basic functions of detergents such as shampoo. Their value as commodities is thus remarkably deteriorated.
Therefore, for detergents containing phosphate surfactants, there has been a demand for improvements in their characteristics, particularly, the foam characteristics.